Our standard panels have a core of Modified Expanded Polystyrene (MEPS). MEPS provides higher R-values per dollar than other types of foam and does not contain chlorofluorocarbons (CFCs), which are believed to damage the Earth's ozone layer. The R-value of MEPS panel cores are extremely stable. In field testing over a number of decades MEPS has been shown to retain virtually all of its original thermal and physical properties. In fact, foam has a unique Thermal Warranty. Another advantage is the fact that the insulative value of MEPS actually increases as the temperature drops. The opposite occurs with fibrous insulations.